Numerous movable craft use electrical energy and are equipped with batteries, for example electric vehicles, work platforms, pallet trucks, etc. These craft generally comprise on-board chargers, i.e. electric battery chargers that are directly mounted on the movable craft. They can also be used with an external battery charging device.
The main function of these chargers is to recharge batteries from the electricity available on the electricity distribution network. They therefore convert an alternating current into a direct current.
The required criteria for the chargers, and more particularly for on-board chargers, are high output, low spatial requirement, galvanic isolation, good reliability, operating safety, low emission of electromagnetic interference and a low rate of harmonics on the input current.
In order to implement the AC-DC conversion function with galvanic isolation, the use of a structure with two converters is known:
a first AC-DC converter, referred to as pre-regulator, which comprises a power factor correction circuit in order to limit the input current harmonics;
a second DC-DC converter for regulating the charge. This DC-DC converter also provides the galvanic isolation function for operating safety.
The first converter generally delivers a constant output voltage and the second converter regulates the voltage and the output current that supply the battery.
Such a system is satisfactory for certain applications such as the power supply for low-power devices (plasma screen or LCD screen television sets, for example). Within the context of the power supply for batteries of motorised devices of the electric motor vehicle type, where the delivered power is significantly higher, the charging device must adapt to the significant variability in the voltage and in the output current supplying the battery.
Due to this variability in the output conditions, the DC-DC converter is used over a wide range of conditions, and particularly in sub-optimal conditions, where the performance of the system is degraded. Such degradation is particularly damaging given the high power that is used.
A requirement therefore exists for improving the performance of charging devices designed to supply batteries of motorised devices, and electric motor vehicles in particular.